1. Field of the Invention
The present invention relates to measurement of rotation rates of a rotor, and more particularly to the phase interference of counterrotating acoustic waves as a measure of rotation rates.
2. Description of the Prior Art
For very accurate rotation measurements, such as in gyroscopes, previous devices used some sort of marking of the surface of the rotor. The marking could be either visual or a distortion of the rotor surface which would be detected, as by a capacitor pickup. The distortion introduced a perturbation to the rotor which created errors in the functioning of the device.
Acoustic waves, being slow compared to electromagnetic waves, can experience greater velocity perturbations due to the velocity being close to that of the rotor surface linear velocity, and eliminate the requirement of marking the rotor with the resulting perturbation.